I think if they really have junior high school level English skills, that would be great. You can express almost every things in English that you learn at junior high school.
I don't think the results are special. Every subjects would be the same. Most students would forget what they have learned after taking tests. That's the way it is. You may know that.
I don't think English education at school in Japan should be changed. You can learn English grammar and you can learn English words at school. That would be enough.
If you want to improve your English skills, just practice hard like sports. English is no exception to this rule.